Drought stress and fluctuating asymmetry in Quercus undulata leaves: confounding effects of absolute and relative amounts of stress?

One of the most general types of stress experienced by plants is water-limitation, which becomes particularly pronounced during periods of drought. We evaluated fluctuating asymmetry (FA) in Quercus undulata leaves for two subsequent dry years: 2001, when precipitation was 25% below average, and 2002, when precipitation was 65% below average, from a plot receiving ambient water and one in which water was excluded. In the first and less severe drought year, ambient-water trees had a slightly higher index of FA than the water-exclusion trees, contrary to expectations. However, in the second and much more extreme drought year, water-exclusion trees exhibited greater FA as expected, but in additional observations water-supplement trees exhibited by far the greatest amount of FA, contrary to expected. Further data on plant water potential confirmed that degree of plant stress corresponded to plot treatments: water exclusion4ambient water4water supplement. Stable carbon isotope ratios indicated that trees on the water-supplement plots were less stressed than ambient-water and water-exclusion trees, and leaf size was much greater for water-supplement trees than ambient-water or water-exclusion trees. We see front matter r 2005 Elsevier Ltd. All rights reserved. .jaridenv.2004.11.010 nding author. Tel.: +1505 667 5659; fax: +1 505 667 0731. dress: [email protected] (J.M. Fair).